This invention concerns pipettes suitable for delivering precise volumes of fluid.
In laboratory experiments in the fields of chemistry, microbiology and biochemistry, it is often necessary to transport an exact quantity of fluid from one vessel to another. Depending on the nature of the experiment being conducted, the quantity of fluid added or removed is very often critical, and a mistake in quantity can lead to confusing, if not erroneous or detrimental, results. Where the quantities of fluid are relatively small, pipettes are utilized to facilitate the addition or removal of the fluid.
The typical prior art graduated dispensing pipette consists of a hollow cylindrical glass or plastic tube. A scale is very often etched, printed, or otherwise placed on the surface of the tube. The pipette scale correlates the height of the fluid column to the quantity of fluid to be dispensed therefrom. The pipette is used by applying suction to its top end, or mouthpiece, allowing an excess quantity of fluid into the pipette and then allowing the fluid to drain to the desired level. By placing a finger over the mouthpiece the user creates a pressure differential across the fluid column and prevents escape of the fluid until the finger is removed. The user can control the rate of flow through the pipette by varying the pressure which his finger exerts on the mouthpiece. Further, the bottom end of the tube, or pipette tip, is typically constricted to control the exit flow rate of the fluid.
Graduated dispensing pipettes, e.g., serological pipettes, are manufactured with specified internal barrel diameters (IDs). The ID determines the volume contained within a given length pipette and therefore sets the spacing between the volumetric graduation markings on the pipette. A number of commercial serological pipettes are available to deliver maximum volumes of either 0.1, 0.2, 1.0, 2.0, 5.0, 10.0, 25.0, or 50.0 milliliters of fluid.
Farnham, U.S. Pat. No. 898,456, describes a double-ended tube for measuring volumes of medicine. The tube has one half calibrated in drops and the other half calibrated in teaspoons. In use, the tube "is changed end for end" when the user desires to measure drops rather than teaspoons, or vice versa.
Graham et al., U.S. Pat. No. 3,058,352, describes a standard pipette for accurately measuring 5 ml of fluid. The pipette has a conical delivery end, not calibrated for accurate measurement, and a cylindrical neck at the other end to allow control of fluid delivery by a person's hand.
Morrill, U.S. Pat. No. 3,441,384, describes a pipette having a relatively flat cross section so that more accurate volumes of fluid may be delivered.
Bellco Glass Inc. in a 1978 product catalog, offers a large diameter 25 ml graduated pipette having a lower portion of a reduced diameter to allow entry and "removal of media from all standard plastic culture flasks" (such flasks have restricted neck openings).